I like that Teamsight helps you manage projects with all of your team members. It allows me to keep track of my time spent, and it gives me a dashboard view from which to analyze where I'm spending the most time. I also really like that it's built-in with TFS so there isn't much else we have to purchase to be able to use this. I dislike not being able to customize some of the information within Teamsight.
For example, I would like to see if a person is blocked or not in terms of time spent on each task. This information doesn't show up in the dashboards, but only shows up when reviewing individual tasks or hours on a task. This is a great tool for tracking project progress, as well as helping to visualize what is taking up the most time on any.